The general procedure for the synthesis of 2,9-dimethylquinolo[2,3-B]acridine-7,14(5H,12H)-dione from 2,5-bis[(4-methylphenyl)amino]-1,4-benzenedicarboxylic acid is as follows: a thermocouple and a condenser (which constitutes a distillation apparatus) were fitted in a 1 L three-neck flask equipped with an electrically heated magnetic stirrer. 84.5 g of polyphosphoric acid (PPA, 0.25 mol) was added to the flask and preheated at 100 °C for 3 hours. Subsequently, 18.8 g of 2,5-bis[(4-methylphenyl)amino]-1,4-benzenedicarboxylic acid (0.05 mol) was added, and the reaction temperature was raised to 125 °C for 3 h before the reaction was stopped. The final crude product 2,9-dimethylquinolo[2,3-B]acridine-7,14(5H,12H)-dione was obtained 16.93 g in 99.59% yield.
